Porous films and processes for the production thereof

Abstract

There are provided a porous film comprising a polymer composition comprising (a) a polymer having C═C double bond and an aliphatic ring having 5 to 10 carbon atoms in a main chain thereof; and (b) another resin; a porous film, wherein all or a part of C═C double bond in the (a) polymer is disappeared; and a porous film, wherein the (a) polymer and the (b) resin are cross-linked therebetween. The porous film has appropriate porosity, air permeability and puncture strength, and is especially excellent in latent heat resistance or heat resistance. Further, there are provided a process for producing the porous film; a separator for a battery comprising the porous film; and a battery comprising the separator.

What is claimed is:  
     
       1. A porous film comprising a polymer composition comprising (a) a polymer having C═C double bond and an aliphatic ring having 5 to 10 carbon atoms in a main chain thereof; and (b) an ultra-high molecular polyethylene having a weight-average molecular weight of 500000 or more, wherein said polymer (a) and said ultra-high molecular polyethylene (b) are crosslinked therebetween. 
     
     
       2. The porous film according to  claim 1 , wherein said (a) polymer is a ring opening polymer of an unsaturated condensed alicyclic compound. 
     
     
       3. The porous film according to  claim 2 , wherein said unsaturated condensed alicyclic compound is norbornene or a norbornene derivative. 
     
     
       4. The porous film according to  claim 1 , wherein a content of said (a) polymer is 0.5 to 70% by weight, and wherein a content of said ultra-high molecular polyethylene (b) is 30 to 99.5% by weight, in the polymer composition. 
     
     
       5. A porous film comprising said (a) polymer and said ultra-high molecular polyethylene (b) of  claim 1 , all or a part of C═C double bond in said (a) polymer being disappeared. 
     
     
       6. The porous film according to  claim 5 , wherein all or a part of C═C double bond in a norbornene ring opening polymer is disappeared. 
     
     
       7. The porous film according to  claim 1 , wherein a norbornene ring opening polymer and said ultra-high molecular polyethylene are cross-linked therebetween. 
     
     
       8. A process for preparing the porous film of any one of claims  5 ,  6  and  7 , characterized by heat-treating the porous film of  claim 1  in the presence of oxygen. 
     
     
       9. A separator for a battery comprising the porous film of  claim 1 . 
     
     
       10. A battery comprising the separator of  claim 9 . 
     
     
       11. The porous film according to  claim 1 , wherein said porous film has a puncture strength of at least 350 gf/25 μm. 
     
     
       12. The porous film according to  claim 1 , wherein the porous film has an air permeability of 100 to 2,000 seconds/100 cc.